1. Field of Invention
The present invention relates to a speed reducer with a shock absorber which can be used with electrical equipment mounted on automobiles and the like.
2. Description of Related Art
In general, some related speed reducers are provided with a rubber damper disposed in a power transmission path from a worm wheel meshed with a worm gear to which a driving force of a motor is transmitted, to a power output shaft as known from Japanese Unexamined Patent Publication No. 60-73982 and Japanese Unexamined Utility Model Publication No. 62-82457. These speed reducers are arranged such that a rubber damper is interposed between a pair of wheels which confront each other with an interval defined therebetween and the confronting surfaces of the rubber damper and the wheels are integrally bonded. In these speed reducers, however, since the rubber damper is twisted at both the ends thereof in an axial direction, if both the plates are insufficiently bonded to the rubber damper, not only is there a possibility that the rubber damper is stripped from the wheels, but also there is a factor for making it difficult to reduce the weight of the speed reducers because a strong metal sheet must be employed as the wheels and the power output shaft must be journaled by a casing through a dedicated bearing.
The inventors of the present invention previously proposed a speed reducer in Japanese Utility Model Application No. 3-55728 (Japanese Unexamined Utility Model Publication No. 5-1054) to solve the defect of the above prior art. The speed reducer is arranged such that a pair of wheels confronting each other in an axial direction have sides which project therefrom in a confronting direction. The projecting sides are spaced from each other with an interval defined between them in an axis-rotational direction to permit rubber dampers to be disposed in the interval. With this arrangement, the rubber dampers are pressed in the axis-rotational direction by the projecting sides to absorb shock. In this case, when the side projecting from one of the wheels acts as a presser for pressing the dampers, the side projecting from the other of the wheels acts as a pressure receiver for receiving the dampers. However, the speed reducer has a drawback that since the rubber dampers which perform a shock absorbing action are essentially only being used to half of their capabilities, a shock absorbing effect is low and there is a waste of shock absorbing ability. This is because the shock absorbing action achieved by the speed reducer is such that when it is assumed that a load from one of the projecting sides acts on the other projecting side as with a clockwise load, no load acts on the rubber damper on the counterclockwise side of the one of the projecting sides and only the rubber damper on the clockwise side thereof is pressed.
To overcome this drawback, the inventors of the present invention proposed a speed reducer in Japanese Patent Application No. 5-156221 (Japanese Unexamined Patent Publication No. 6-341493) which is arranged such that first and second projections projecting from first and second wheels, respectively, are disposed together in the respective intervals of a plurality of shock absorbing rubber dampers so that all the rubber dampers perform a shock absorbing action.
In the speed reducer arranged as described above, however, the first and second projections located together in an arbitrary interval must be disposed in parallel with each other in a diametrical direction so that any of them can directly compress the rubber dampers (compression is securely executed by any one of them). Thus, the surfaces of the rubber dampers are partially compressed by the respective projections and the compressed surfaces are unevenly distributed in the diametrical direction and as a result the respective rubber dampers are deformed in a strained state without being evenly compressed and deformed, which is a problem to be solved by the present invention.
Further, it is also a problem to be solved by the present invention to reduce the number of parts as much as possible in the solution of the above problems.